Curling
Upward lifting of slab edges and corners caused by the top of the slab drying and shrinking faster than the bottom, which stays moist.
What does curling mean?
The differential shrinkage between top and bottom bends the slab, lifting edges off the base and leaving them unsupported. Curled edges then crack under wheel loads and joints spall as traffic hammers the unsupported panels. Contributing factors include high-shrinkage mixes, thin slabs, wide joint spacing, hard troweling, and a vapor retarder directly under the slab that prevents downward drying.
In practice
In a warehouse, forklift wheels slapping at every joint usually means the panel edges have curled and lost support.